The diaphragmatic sphincter and hiatus hernia

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Endoscopic and radiographic studies suggest that 50-94% of patients with gastroesophageal reflux disease (GERD) have a type-I hiatal hernia while the corresponding prevalence in control subjects ranges from 13-59% [37]-[40]. Most patients with severe esophagitis have a hiatal hernia [41], [42] and 96% of patients with Barretts esophagus have a > 2 cm hiatus hernia [43]. However, the importance of a type-I hiatal hernia is obscured by the misconcep tion that this is an all or none phenomenon. It is more useful to view type-I hiatal hernia as a continuum of progressive disruption of the gastroesopha-geal junction, as illustrated in Fig. 6. Type-I hiatus hernia impacts on reflux both by affecting the competence of the gastroesophageal junction in preventing reflux and in compromising the process of esophageal acid clearance once reflux has occurred.

Physiological studies by Mittal have clearly demonstrated that the augmentation of EGJ pressure observed during a multitude of activities associated with transient increases in intra-abdominal pressure is attributable to contraction of the crural diaphragm [44]. With hiatus hernia, crural diaphragm function is potentially compromised both by its axial displacement (1) and potentially by atrophy consequent from dilatation of the hiatus [45]. The impact of hiatus hernia on EGJ susceptibility to reflux elicited by straining maneuvers was demonstrated in studies in normal volunteers compared to

Table 1. Factors that influence lower esophageal sphincter pressure and tLESR frequency

Increase

Decrease

Increase transient

Decrease transient

LES pressure

LES pressure

LES relaxations

LES relaxations

Foods

Ethanol

Peppermint

Fat

Medications

Metoclopramide

Nitrates

Sumatriptan

Atropine

Domperidone

Calcium channel blockers

Morphine

Prostaglandin F2a

Loxiglumide

Morphine

Meperidine

Diazepam

Barbituates

Hormones and

Gastrin

Secretin

Cholecystokinin

Baclofen

neural agents

Motilin

Cholecystokinin

L-arginine

L-NAME

Substance P

Glucagon

Serotonin

a-Adrenergic agonists

Gastric inhibitory polypeptide

^-Adrenergic antagonists

Vasoactive intestinal polypeptide

Cholinergic agonists

Progesterone a-Adrenergic antagonists ^-Adrenergic agonists Cholinergic antagonists Serotonin

GERD patients with and without hiatus hernia [34]. Of several physiological and anatomical variables tested, the size of hiatus hernia was shown to have the highest correlation with the susceptibility to strain-induced reflux (Fig. 7). The implication of this observation is that patients with hiatus hernia exhibit progressive impairment of the diaphragmatic component of EGJ function proportional to the extent of axial herniation [1].

Another effect that hiatus hernia exerts on the anti-reflux barrier is to diminish the intraluminal pressure within the EGJ. Relevant animal experiments revealed that simulating the effect of hiatus hernia by severing the phrenoesophageal ligament reduced the LES pressure and that the subsequent repair of the ligament restored the LES pressure to levels similar to baseline [46]. Similarly, manometric studies in humans using a topographic representation of the EGJ high pressure zone of hiatus hernia patients revealed distinct intrinsic sphincter and hiatal canal pressure components, each of which was of lower magnitude

LES pressure (mmHg)

Fig. 7. Model of the relationship between the lower esophageal sphincter (LES) pressure, size of hernia, and the susceptibility to gastroesophageal reflux induced by provocative maneuvers as reflected by the reflux score on the Z-axis.The overall equation of the model is: reflux score- = 22.64 + 12.05 (hernia size) - 0.83 (LES pressure) - 0.65 (LES pressure X hernia size).The hernia size is in cm,and the LES pressure is in mmHg.The multiple correlation coefficient of this equation for the 50 subject data set was 0.86 (R2 = .75). Thus, the susceptibility to stress reflux is dependent upon the interaction of the instantaneous value of LES pressure and the size of the hiatus hernia (From [34]: Sloan S, Rademaker AW,Kahrilas PJ (1992) Determinants of gastroesophageal junction incompetence: hiatal hernia,lower esophageal sphincter,or both? Ann Intern Med 117: 977-982,with permission)

LES pressure (mmHg)

Fig. 7. Model of the relationship between the lower esophageal sphincter (LES) pressure, size of hernia, and the susceptibility to gastroesophageal reflux induced by provocative maneuvers as reflected by the reflux score on the Z-axis.The overall equation of the model is: reflux score- = 22.64 + 12.05 (hernia size) - 0.83 (LES pressure) - 0.65 (LES pressure X hernia size).The hernia size is in cm,and the LES pressure is in mmHg.The multiple correlation coefficient of this equation for the 50 subject data set was 0.86 (R2 = .75). Thus, the susceptibility to stress reflux is dependent upon the interaction of the instantaneous value of LES pressure and the size of the hiatus hernia (From [34]: Sloan S, Rademaker AW,Kahrilas PJ (1992) Determinants of gastroesophageal junction incompetence: hiatal hernia,lower esophageal sphincter,or both? Ann Intern Med 117: 977-982,with permission)

than the EGJ pressure of a comparator group of normal controls [47] (Fig. 1). However, simulating reduction of the hernia by arithmetically repositioning the intrinsic sphincter back within the hiatal canal resulted in calculated EGJ pressures that were practically indistinguishable from those of the control subjects. Along with previous investigations these data also demonstrated that hiatus hernia reduced the length of the EGJ high pressure zone [1]. This is likely due to disruption of the EGJ segment distal to the SCJ attributable to the opposing sling and clasp fibers of the gastric cardia [2].

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